Surface plasmon-based nanosensors and systems and methods for sensing photons and chemical or biological agents

ABSTRACT

Surface plasmon-based nanosensor, comprising: at least one first element of metal, preferably silver or gold, or of semiconductor, the first element being excitable to surface Plasmon resonance, in particular localized surface plasmon resonance, in the presence of electromagnetic radiation from a source, and at least one second element preferably near the first element that in the presence of the electromagnetic radiation is exciton-plasmon coupled to the first element and emits electromagnetic radiation representative of the exciton-plasmon coupling, and systems and methods for sensing photons and chemical or biological agents.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of and claims priority under 35U.S.C. 120 to co-pending commonly owned U.S. application Ser. No.14/168,051, filed 30 Jan. 2014, which in turn is related to and claimspriority under 35 U.S.C. §119 to European Application No. 13159918.5,filed 19 Mar. 2013, the entirety of which is hereby incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to surface plasmon-based nanosensors, asystem for sensing photons, a system for sensing chemical or biologicalagents, a method for sensing photons and a method for sensing chemicalor biological agents.

BACKGROUND

Nano-scale systems have demonstrated many novel and interesting opticalproperties. These systems are extremely important for futurephoton-based devices among many other applications. One of the mostimportant nano-devices are nanosensors.

SUMMARY

It is the object of the present invention to provide a nanosensor thatis small, but yet sensitive to weak electromagnetic signals/fields orchanges thereof.

This aim is achieved by a surface plasmon-based nanosensor, comprising:at least one first element of metal, preferably silver or gold, or ofsemiconductor, the first element being excitable to surface plasmonresonance, in particular localized surface Plasmon resonance, in thepresence of electromagnetic radiation from a source, and at least onesecond element preferably near the first element that in the presence ofthe electromagnetic radiation is exiton-plasmon coupled to the firstelement and emits electromagnetic radiation representative of theexiton-plasmon coupling. Said nanosensor might be called “a plasmonicsensor” as well and can be categorized as an optical sensor. The atleast one first element and the at least one second element are usuallydifferent.

According to further a further aspect, this aim is also achieved by asystem for sensing photons of electromagnetic radiation from an externalsource, comprising: a surface plasmon-based nanosensor according to anyone of claims 1 to 3 and a detector for detecting electromagneticradiation emitted by the second element in response to electromagneticradiation from an external source.

Further, according to further aspect the invention provides a system forsensing chemical or biological agents, comprising: a surfaceplasmon-based nanosensor according to claim 3 or 4, and a detector fordetecting electromagnetic radiation emitted by the second element inresponse to the electromagnetic radiation from an external source or theinternal source with a chemical or biological agent in direct orindirect contact with the at least one first element, in particularfurther comprising an evaluation unit for evaluating the identity of thechemical or biological agent based on the detected electromagneticradiation.

This aim also achieved by a surface plasmon-based nanosensor,comprising: at least one first element of metal, preferably silver orgold, or of semiconductor, the first element being excitable to surfaceplasmon resonance, in particular localized surface plasmon resonance, inthe presence of electromagnetic radiation from a source and at least onesecond element preferably near the first element for exciting surfaceplasmon resonance of the at least one first element.

The invention also provides a system for sensing photons ofelectromagnetic radiation from an external source, comprising: a surfaceplasmon-based nanosensor according to any one of claims 8 to 10, apumping unit for pumping the at least one second element and a detectorfor detecting the total electromagnetic radiation emitted by the atleast first element and the at least one second element in response toelectromagnetic radiation emitted by an external source or the internalsource and incident on the at least one first element and the at leastone second element, in particular further comprising an evaluation unitfor evaluating the statistics, in particular the frequency and/or theintensity and/or photon number, of the electromagnetic radiation fromthe external source based on the detected electromagnetic radiation.

Further, this aim is achieved by a system for sensing chemical orbiological agents, comprising: a surface plasmon-based nanosensoraccording the claim 10 or 11, a pumping unit for pumping the at leastone second element and a detector for detecting the totalelectromagnetic radiation emitted by the at least one first element andthe at least one second element in response to the electromagneticradiation emitted by an external source or the internal source andincident on the at least one first element and the at least one secondelement with a chemical or biological agent in direct or indirectcontact with the at least one first element.

The present invention is also directed to the use of a nanosensoraccording to any one of claims 1 to 3 or 8 to 10 or of a systemaccording to claim 5 or 12 for sensing photons and the use of ananosensor according to claim 3,4,10 or 11 or of a system according toclaim 6 or 13 for sensing chemical or biological agents.

The present invention also provides a method for sensing photons ofelectromagnetic radiation from a source, comprising: irradiating atleast one first element of metal, preferably silver or gold, or ofsemiconductor, excitable to surface plasmon resonance, in particularlocalized surface plasmon resonance, with electromagnetic radiation froma source for exciting surface plasmon resonance on said at least onefirst element, providing for exciton-plasmon coupling between the atleast one first element and at least one second element and for emissionof electromagnetic radiation by the at least one second element, anddetecting the electromagnetic radiation emitted by the at least onesecond element.

Also, the present invention provides a method for sensing photons ofelectromagnetic radiation from a source, comprising: irradiating atleast one first element of metal, preferably silver or gold, or ofsemiconductor, excitable to surface plasmon resonance, in particularlocalized surface plasmon resonance, and at least one second elementwith electromagnetic radiation from a source, the at least one secondelement being pumped by pumping unit for exciting surface plasmonresonance on or in the at least first element and detecting the totalelectromagnetic radiation emitted by the exiton-plasmon coupled pumpedat least one second element and at least one first element.

In addition, the present invention provides a method for sensingchemical or biological agents, comprising: directly or indirectlycontacting at least one first element of metal, preferably silver orgold, or of semiconductor, excitable to surface plasmon resonance, inparticular localized surface plasmon resonance, with a sample comprisinga chemical or biological agent to be sensed, irradiating the at leastone first element with electromagnetic radiation from an internal orexternal source for exciting surface plasmon resonance on said at leastone first element, providing for exciton-plasmon coupling between the atleast one first element and the at least one second element and foremission of electromagnetic radiation by the at least one secondelement, and detecting the electromagnetic radiation emitted by the atleast one second element.

Finally, the present invention provides a method for sensing chemical orbiological agents, comprising: directly or indirectly contacting atleast one first element of metal, preferably silver or gold, or ofsemiconductor, excitable to surface plasmon resonance, in particularlocalized surface plasmon resonance, with a sample comprising a chemicalor biological agent to be sensed, irradiating the at least one firstelement and the at least one second element with electromagneticradiation from a source, the at least one second element being pumped bya pumping unit for exciting surface plasmon resonance on said at leastone first element and detecting the total electromagnetic radiationemitted by the exciton-plasmon coupled pumped at least one secondelement and at least one first element.

According to a special embodiment of the nanosensor according to claim1, the at least one first element is a nanoparticle and/or the at leastone second element is quantum dot. More generally, the second elementcould be a two-level-system (TLS).

Preferably the at least one second element is preferably totallyembedded in a matrix of Photonic or Polaritonic Band-gap (PGB)-material,preferably silicon carbide (SiC), and/or wherein the at least one firstelement is at least or only partially or totally embedded in a matrix ofPhotonic or Polaritonic Band-gap (PGB)-material, preferably siliconcarbide (SiC).

A further special embodiment is characterized in further comprising aninternal source capable of emitting the electromagnetic radiation. Suchan embodiment would be well suited for use of the nanosensor as abio-sensor for sensing biological or chemical agents (analytes).

Conveniently, the system comprises a shielding for shielding the atleast one second element against external electromagnetic radiation.

According to a special embodiment of the nanosensor according to claim8, the at least one first element is a nanoparticle and/or the at leastone second element is a quantum dot. More generally, the at least onesecond element might be a two-level-system (TLS).

Preferably, the at least one second element is preferably totallyembedded in a matrix of Photonic or Polaritonic Band-gap (PGB)-material,preferably silicon carbide (SiC), and/or wherein the at least one firstelement is at least or only partially or totally embedded in a matrix ofPhotonic or Polaritonic Band-gap (PGB)-material, preferably siliconcarbide (SiC).

In particular when being used as a biological sensor (bio-sensor) orchemical sensor, it might further comprise an internal source capable ofemitting the electromagnetic radiation.

Conveniently the method according to claim 16 or 17 further comprisesevaluating the statistics, in particular the frequency and/or intensityand/or photon number, of the electromagnetic radiation from the sourcebased on the detected electromagnetic radiation.

Finally, conveniently the method according to claim 19 or 20 furthercomprises identifying the identity of the chemical or biological agentbased on the detected electromagnetic radiation.

The present invention is based on the unexpected conclusion that by wayof using the phenomenon of surface plasmon resonance weakelectromagnetic radiation/signals or signal changes can be enhanced andcan be made (easier) detectable.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become clear fromthe claims and following description, in which embodiments of theinvention are illustrated in detail with reference to the schematicdrawings:

FIG. 1 shows a scheme of a system for sensing photons of electromagneticradiation from an external source according to a first specialembodiment of the invention;

FIG. 2 shows a scheme of a system for sensing photons of electromagneticradiation from an external source according to a second specialembodiment of the invention;

FIG. 3 shows a scheme of a system for sensing chemical or biologicalagents according to a first special embodiment of the invention; and

FIG. 4 shows a scheme of a system for sensing chemical or biologicalagents according to a second special embodiment of the invention.

DETAILED DESCRIPTION

The system 10 of FIG. 1 for sensing photons of electromagnetic radiationfrom an external source comprises a surface plasmon-based nanosensor 12.Said nanosensor 12 comprises a nanoparticle 14 of metal, e.g. silver orgold, or of semiconductor as a first element. The nanoparticle 14 isexcitable to surface plasmon resonance, in particular localized assurface plasmon resonance, in the presence of electromagnetic radiation16 from an external source (not shown). Furthermore, the nanosensor 12comprises a quantum dot 18. A quantum dot is normally a nanometer sizedsemiconductor region within another material of larger Band-gap. Inparticular, the quantum dot 18 with diameter d₂ is situated in adistance of R to the nanoparticle 14 with the diameter d₁. The quantumdot 18 will be exciton-plasmon coupled to the nanoparticle 14 in thepresence of the electromagnetic radiation 16 and will emitelectromagnetic radiation 20 representative of the exciton-plasmoncoupling.

The nanosensor 12 and the quantum dot 18 are embedded in PGB-material22.

The system 10 further comprises a detector (not shown) for detecting theelectromagnetic radiation 20 emitted by the quantum dot 18 in responseto the electromagnetic radiation 16 from the external source (notshown). Also, said system 10 comprises an evaluation unit (not shown)for evaluating the statistics, in particular the frequency and/or theintensity and/or the photon number, of the electromagnetic radiation 16from the external source (not shown). Preferably, the system 10comprises a shielding (not shown) for shielding the quantum dot 18against external electromagnetic radiation, in particular the externalelectromagnetic radiation 16.

By way of the nanosensor 12 and the system 10 photons—perhaps evensingle photons—can be detected within very narrow spectral width andprovide statistical information about them, e.g. photon numbers. ThePBG-material 22, e.g. silicon carbide, improves the preciseness of thedetection of photons with certain frequency ranges. But the PBG-materialis not a must. PBG-materials are characterized as having a gap in theirdispersion relation characterized by an upper and lower energy band,corresponding to frequencies of light that are forbidden to propagatewithin the PBG-medium.

The system 10 can be described as made of a receiver or signaltransformer, the quantum dot 18, situated near or close to thenanoparticle 14 that works as a photon collector. When photons of theelectromagnetic radiation 16 from the external source (not shown) hitthe nanoparticle 14, they excite certain plasmon modes that depend onthe frequency of the photons and on the shape and material of thenanoparticle 14. These plasmons, in turn, generate a certain dipolemoment, which, and through the near-field, will couple to thetransformer (quantum dot 18), which will also generate a dipole momentthat is proportional in magnitude to that of the nanoparticle 14 whichin turn is proportional to the frequency and intensity of the incidentelectromagnetic radiation 16. The transformer (quantum dot 18) willtransform the signal coming from the nanoparticle 14 into a morereadable signal, e.g. electrical signal, through the populationinversion that will occur within the transformer's (quantum dot)electronic states. This population difference carries within it thestatistical properties of the incoming photons.

The usage of the PBG-material 22 has the effect of increasing thesensitivity of the nanoparticle 14 to the frequency of the incidentelectromagnetic radiation 16.

The system 10 can be used to detect specific signals, especially thoseclose to the plasmon frequency of the nanoparticle 14 as these plasmonsresonate, almost spontaneously, at their natural frequency leading to alarge induced dipole moment in the nanoparticle 14 and consequently astronger signal will be transmitted. In fact, the whole “system” can betuned such that to resonate with very narrow frequency range. This canbe done by designing the nanoparticle 14 and the quantum dot 18 suchthat they only resonate at a specific frequency, e.g. by choosing anelongated of spheroid nanoparticle for example instead of spherical.

Moreover, by changing the material and/or shape of the nanoparticle 14it is possible to change its natural plasmonic frequency andconsequently fine tune the “system” to be responsive to certain lightfrequencies, even if the intensity of the light is weak, as inelectromagnetic signals emitted from for example some biologicalentities. The nanoparticle 14 can come in any shape, configuration andmaterial.

The above configuration can be put in any other medium or configurationto produce the results desirable by the experimenter or manufacturer.

Even though in FIG. 1 spherical elements (nanoparticle 14 and quantumdot 18) are shown, this is not necessary. The elements can take anyshape for getting the desired results. The nanoparticle 14 can havenon-isomorphic shape that can support multiple plasmon resonances. Thus,by tuning the exciting element (nanoparticle) to these resonances,photons with different frequencies can be detected. It is also to benoted that ensembles of nanoparticles and/or quantum dots can be used.

A more readable signal is the usual electric signal that mostelectronics are using in their operations.

Every nanoparticle will have a specific plasmonic resonance frequencybased on its shape and material and the surrounding material. The morethe incoming/incident electromagnetic radiation, for example light, isin resonance with the plasmonic frequency, the more responsive thenanoparticle's electrons will be and the larger the dipole momentgenerated by the oscillations of the electrons will be. Consequently,the exciton plasmon coupling between the nanoparticle and the receiver,e.g. quantum dot 18, will be stronger. The outcome signal(electromagnetic radiation 20) from the quantum dot 18 depends on thiscoupling, labelled omega.

Thus, the coupling between the nanoparticle 14 and the quantum dot 18depends on the dipole moments of the nanoparticle 14 and the quantum dot18, which in turn depends on the frequency of the incidentelectromagnetic radiation 16. In addition, and as the below equationindicates, the signal lamda(p) coming out of the quantum dot 18 dependson the intensity of the electromagnetic radiation 16, which isproportional to the number of photons carried in the electromagneticradiation 16. Thus, from the below equation, if lambda(p) is known, theother statistics of the electromagnetic radiation 16 (external field)can also be deduced.

${Ap} = {\frac{2}{1 - \Sigma_{z}} \times \{ {\frac{4\; {GKI}}{( {1 - {\frac{2\; G}{\gamma \; Z_{0}}\Sigma_{z}}} )^{2}} + {\gamma_{2}Z_{2}} + {\gamma_{c}\Sigma_{z}}} \}}$

Here, γ₂,γ are the decay constant of the quantum dot 18 and nanoparticle14, respectively, γ_(c)=γ₂Z₂ ²(2n_(c)+1) and n_(c) is the average numberof quanta in the C-reservoir. Z₀ and Z₂ are the form constants of thenanoparticle 14 and the quantum dot 18, respectively, which are relatedto the PBG-material 22.

$G = \frac{2\Omega}{\gamma_{c}}$

with Omega being the coupling constant of the quantum dot 18 and thenanoparticle 14 which depends on the relative values of their dipolemoments μ₂ and μ₀, Σ_(Z) is the population inversion between theelectronic states of the quantum dot 18.

$K = \frac{4\mu_{0}^{2}}{\gamma \; Z_{0}^{2}\hslash^{2}}$

and I is the intensity of the field and is proportional to the number ofphotons.

The signal provided by the quantum dot 18 is an optical signal, becausethe electronic/electrons of the quantum dot 18 is/are excited to ahigher state, when it de-excites, it will emit a photon/photons. It isup to the experimentalist or the manufacturer to decide what to do withthis photon/these photons, for example keep it/them this way, amplifyingit/them or turning it/them into an electronic signal, etc. It is theelectromagnetic radiation 16 that pumps the nanoparticle 14 which inturn will excite a population inversion in the electronic states of thequantum dot 18 and consequently produces the final signal.

FIG. 2 shows a further special embodiment of a system 24 for sensingphotons of electromagnetic radiation from an external source (notshown). Said system 24 comprises a surface plasmon-based nanosensor 26.Said nanosensor 26 comprises a nanoparticle 28 of metal, preferablysilver or gold, or of semiconductor, as a first element. Saidnanoparticle 28 is excitable to surface plasmon resonance, in particularlocalized surface plasmon resonance, in the presence of electromagneticradiation from a source. Furthermore, said nanosensor 26 comprises aquantum dot 30 as a second element for exciting surface plasmonresonance of the nanoparticle 28. In the present example, the diameterd₁ of the nanoparticle 28 is the same as the diameter d₁ of thenanoparticle 14, the diameter d₂ of the quantum dot 30 is the same asthe diameter d₂ of the quantum dot 18 and the distance between thenanoparticle 28 and the quantum dot 30 is R and the same as the distanceR between the nanoparticle 14 and the quantum dot 18. The nanoparticle28 and the quantum dot 30 are totally embedded in PGB-material 22.

The system 24 further comprises a pumping unit (not shown) for pumpingthe quantum dot 30 by way of electromagnetic radiation 32 and a detector(not shown) for detecting the total electromagnetic radiation 34 emittedby the nanoparticle 28 and the quantum dot 30 in response toelectromagnetic radiation 36 emitted by an external source (not shown)and incident on the nanoparticle 28 and the quantum dot 30.

In addition, said system 24 further comprises an evaluation unit (notshown) for evaluating the statistics, in particular the frequency and/orthe intensity and/or photon number, of the electromagnetic radiation 36from the external source (not shown) based on the detected totalelectromagnetic radiation 34.

The configuration of the system 24 is similar to that of the system 10,with the exception, that in the system 24 the quantum dot 30 ispumped/excited by the electromagnetic radiation 32 and will pump theplasmons of the nanoparticle 28 which inturn will emit electromagneticradiation, e.g. light, with certain statistics, frequency and spectralwidth. Applying the electromagnetic radiation 36 to the nanoparticle 28and the quantum dot 30 will induce changes in the properties of theemitted total electromagnetic radiation, e.g. its intensity and spectralwidth. These changes are directly related to the properties of theelectromagnetic radiation 36, e.g. intensity. Thus, from theses changesone can gain information on the applied electromagneticradiation/external field.

Both the system 10 and the system 24 can be used to detect specificsignals, especially those close to the plasmon frequency of thenanoparticle as these plasmons resonate, almost spontaneously, at theirnatural frequency leading to a large induced dipole moment in thenanoparticle and consequently a stronger signal will be transmitted.

For sensing photons with the system 24, the final total emittedsignal/electromagnetic radiation 34 is read and information about theapplied external field/electromagnetic radiation 36 is gathered from it.

FIGS. 3 and 4 show special embodiments of nanosensors and systems forsensing chemical or biological agents (analytes). Said systems aresimilar to the systems 10 and 24, respectively.

In particular, the system 38 comprises a surface plasmon-basednanosensor 40. Said nanosensor 40 comprises a nanoparticle 42 of metal,preferably silver or gold, or of semiconductor, as a first element. Thenanoparticle 42 is excitable to surface plasmon resonance, in particularlocalized surface plasmon resonance, in the presence of electromagneticradiation 44 from a source (not shown). In this example, said sourcemight be external from the nanosensor 40 or inside the nanosensor 40.

Furthermore, the nanosensor 40 comprises a quantum dot 46 near thenanoparticle 42 as a second element. Said quantum dot 46 will beexciton-plasmon coupled to the nanoparticle 42 in the presence of theelectromagnetic radiation 44 and will emit electromagnetic radiation 48representative of the exciton-plasmon coupling. In this example, thenanoparticle 42 and the quantum dot 46 have the same diameter d₁ and d₂,respectively, as the nanoparticle 14 and the quantum dot 18 of FIG. 1.The quantum dot 46 is also totally embedded in PGB-material 50.

However, the nanoparticle 42 is only partially embedded in thePGB-material 50. The nanoparticle 42 protrudes a little bit from thePGB-material 50 into an external medium 52, e.g. buffer solution, thinfilm etc., where the chemical or biological agent (analyte) will besupplied. This is for enabling the nanoparticle 42 to sense the presenceof the external agent 54. This protrusion could effect the plasmonicresonance frequency of the nanoparticle 42 a bit or it may not. Itdepends on how much the nanoparticle 42 is protruding into the externalmedium 52. However, this can be easily accounted for by measuring theplasmon resonance prior to the inclusion of the external agent 54, andonce the agent 54 is supplied, the actual shifting of the plasmonresonance can be measured.

The system 38 further comprises a detector (not shown) for detecting theelectromagnetic radiation 48 emitted by the quantum dot 46 in responseto the electromagnetic radiation 44 with said medium 52 or agent 54 indirect contact with the nanoparticle 42. In addition, said system 38further comprises an evaluation unit (not shown) for evaluating theidentity of the chemical or biological agent 54 based on the detectedelectromagnetic radiation 56.

One idea behind the plasmonic bio nanosensor 40 and the system 38 isthat the resonance of the plasmons is greatly sensitive to thesurrounding environment. In fact, the surface plasmon resonancefrequency depends specifically on the dielectric function of theplasmonic material, e.g. gold and silver, and the surrounding material,e.g. silicon, buffer solution, thin film, etc.

Now when working as a bio-detector, what happens is that when thebiological or chemical agents get into close proximity to the surface ofthe nanoparticle 42, either they will change the permittivity of thesurrounding material (external medium 52), e.g. a buffer solution, orstick to the surface of the nanoparticle 42. In either case they willchange the surrounding conditions of the nanoparticle 42, which in turnwill change the resonance frequency of the surface plasmons, shiftingthem toward for example the red or blue end of the spectrum depending onthe changes induced by the biological or chemical external agent 54.This shifting can be detected and based upon it can determine theidentity of the external agent 54. In the system 38 the external agent54 will change the surface plasmon resonance frequency of thenanoparticle 42 and consequently will change how the nanoparticle 42will interact with the electromagnetic radiation 48, which willtranslate into a change in the signal output of the quantum dot 46. Fromthis change, one can deduce information about the external agent 54. Itshould be noted that the quantum dot 46 should be shielded from theexternal agent 54 to ensure that they will not interfere with the signalcoming out of the quantum dot 46. Otherwise, this interference should beincluded in the final calculations.

The system 58 shown in FIG. 4 comprises a surface plasmon-basednanosensor 60. Said nanosensor 60 comprises a nanoparticle 62 of metal,preferably silver or gold, or of semiconductor, as a first element. Thenanoparticle 62 is excitable to surface plasmon resonance, in particularlocalized surface plasmon resonance, in the presence of electromagneticradiation 64 from an external or internal source (not shown). Further,said nanosensor 60 comprises a quantum dot 66 as a second element nearthe nanoparticle 62 for exciting surface plasmon resonance of thenanoparticle 62. The nanoparticle 62 and the quantum dot 66 have thesame diameter d₁ and d₂, respectively, and are spaced apart by adistance R as the nanoparticle 42 and the quantum dot 46 of the system38. The quantum dot 66 is totally embedded in a PGB-material 68, whereasthe nanoparticle 62 is only partially embedded in said PGB-material 68like the nanoparticle 42 of the system 38.

The system 58 further comprises a pumping unit (not shown) for pumpingthe quantum dot 66 by means of electromagnetic radiation 70 and adetector (not shown) for detecting the total electromagnetic radiation72 emitted by the nanoparticle 62 and the quantum dot 66. Also, saidsystem 58 comprises an evaluation unit (not shown) for evaluating theidentity of the chemical or biological agent 74 (in an external medium76) based on the detected electromagnetic radiation 72.

In the system 58 of FIG. 4, just like in the system 38 of FIG. 3, thechanges induced by the external agent 74 will translate into changes inthe total electromagnetic radiation 72. In fact, on said system 58, andwhen working as a bio-detector, the external agent 74 will shift theplasmon resonance of the nanoparticle 62. This shift will be detectedfrom the statistics of the total electromagnetic radiation, e.g. light,emitted out of the system 58, which was generated from the interactionbetween the pumped quantum dot 66 and the nanoparticle 62. In addition,as in the case of the system 38, it might be much better if the quantumdot 66 is shielded from the external agent 74.

The nanosensor 60 as well the system 58 are simple, small and mobile.Like in the system 38 of FIG. 3, in the system 58 of FIG. 4 andintegrated source of electromagnetic radiation, e.g. light, like ananolaser could be incorporated.

One important factor that determines the efficiency of the nanosensor ishow accurate it is. Plasmonic resonances are fairly narrow. However, thespectrum of the electromagnetic radiation, for example light, emittedfrom the system is usually not narrow due to broadening processes. Thiscould be overcome by the PGB-material 68.

Incorporating the PGB-material into the system will greatly narrow thespectrum of the electromagnetic radiation, e.g. light, emitted from thesystem, rendering the sensing operation much more sensitive andaccurate. However, an ensemble of anyone of the systems described abovemay be necessary to ensure better detecting.

The features disclosed in the foregoing description, in the claimsand/or in the accompanying drawings may, both separately and in anycombination thereof, be material for realising the invention in diverseforms thereof.

REFERENCE LIST

-   -   10 system    -   12 nanosensor    -   14 nanoparticle    -   16 electromagnetic radiation    -   18 quantum dot    -   20 electromagnetic radiation    -   22 PGB-material    -   24 system    -   30 quantum dot    -   26 nanosensor    -   28 nanoparticle    -   32 electromagnetic radiation    -   34 total electromagnetic radiation    -   36 electromagnetic radiation    -   40 system    -   42 nanosensor    -   44 nanoparticle    -   46 electromagnetic radiation    -   46 quantum dot    -   48 electromagnetic radiation    -   50 PGB-material    -   52 external medium    -   64 agent    -   58 system    -   60 nanosensor    -   62 nanoparticle    -   64 electromagnetic radiation    -   66 quantum dot    -   68 PGB-material    -   70 electromagnetic radiation    -   72 total electromagnetic radiation    -   74 agent    -   76 external medium    -   d₁ diameter of nanoparticle 14, 28, 62    -   d₂ diameter of quantum dots 18, 30, 66    -   R distance

1. Surface plasmon-based nanosensor, comprising: at least one firstelement of metal or of semiconductor, the first element being excitableto surface plasmon resonance in the presence of electromagneticradiation from a source and at least one second element for excitingsurface plasmon resonance of the at least one first element. 2.Nanosensor according to claim 1, wherein the at least one first elementis a nanoparticle and/or the at least second element is a quantum dot.3. Nanosensor according to claim 1, wherein the at least one secondelement is embedded in a matrix of Photonic or Polaritonic Band-gap(PGB)-material and/or wherein the at least one first element is at leastpartially embedded in a matrix of Photonic or Polaritonic Band-gap(PGB)-material.
 4. Nanosensor according to claim 1, further comprisingan internal source capable of emitting the electromagnetic radiation. 5.System for sensing photons of electromagnetic radiation from an externalsource, comprising: a surface plasmon-based nanosensor according toclaim 1, a pumping unit for pumping the at least one second element anda detector for detecting the total electromagnetic radiation emitted bythe at least first element and the at least one second element inresponse to electromagnetic radiation emitted by an external source orthe internal source and incident on the at least one first element andthe at least one second element.
 6. System for sensing chemical orbiological agents, comprising: a surface plasmon-based nanosensoraccording to claim 5, a pumping unit for pumping the at least one secondelement and a detector for detecting the total electromagnetic radiationemitted by the at least one first element and the at least one secondelement in response to the electromagnetic radiation emitted by anexternal source or the internal source and incident on the at least onefirst element and the at least one second element with a chemical orbiological agent in direct or indirect contact with the at least onefirst element.
 7. Method for sensing photons of electromagneticradiation from a source, comprising: irradiating at least one firstelement of metal or of semiconductor, excitable to surface plasmonresonance and at least one second element with electromagnetic radiationfrom a source, the at least one second element being pumped by a pumpingunit for exciting surface plasmon resonance on the at least firstelement and detecting the total electromagnetic radiation emitted by theexciton-plasmon coupled pumped at least one second element and at leastone first element.
 8. Method for sensing chemical or biological agents,comprising: directly or indirectly contacting at least one first elementof metal or of semiconductor, excitable to surface plasmon resonancewith a sample comprising a chemical or biological agent to be sensed,irradiating the at least one first element and the at least one secondelement with electromagnetic radiation from a source, the at least onesecond element being pumped by a pumping unit for exciting surfaceplasmon resonance on said at least one first element and detecting thetotal electromagnetic radiation emitted by the exciton-plasmon coupledpumped at least one second element and at least one first element. onesecond element and at least one first element.